Slow Wave Gap Waveguide With Bandpass Filtering Functionality

Compact Wideband Groove Gap Waveguide Bandpass Filters Manufactured with 3D Printing and CNC Milling Techniques

“…Table 5 compares various GGW bandpass filters with the wideband GGW Chebyshev filters manufactured in this work. The order n or number of cells of the GGW filters [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] reported in Table 5 varies between two and seven, and almost half of them are of order five, as are the proposed GGW filters. The structures were mainly manufactured by means of a CNC milling machine, except for two [36,41] that also used a 3D printing technique.…”

“…Half of them are distributed in the low X and Ku bands (8 GHz-18 GHz) as the proposed design. As can be seen in Table 5, unlike the proposed design method and [45], which can achieve wideband responses (FBW > 10%), the other filters developed are narrowband (FBW < 4%), since they were obtained from resonant cavities [30][31][32][33][34][35][36], coupled resonators [37][38][39][40][41][42], evanescent wave coupled resonators [43], and periodic corrugations acting as resonators [44], which can only work in a narrow bandwidth. The wideband response of the proposed GGW bandpass filter design was obtained by combining the high-pass behavior of the GGW with the low-pass characteristic of the metallic pins placed along the groove area of the GGW, acting as impedance inverters.…”

“…Several bandpass filters have been successfully implemented in GGW technology [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Their designs are based on resonant cavities [30][31][32][33][34][35][36], coupled resonators [37][38][39][40][41][42], evanescent wave coupled resonators [43] and periodic corrugations acting as resonators [44].…”

“…Their frequency responses have an FBW lower than 4%. A wideband bandpass filter with FBW = 22.2% has also been proposed, introducing quasi-periodic transverse corrugations inside the GGW [45]. The resulting structures have been manufactured using computer numerical control (CNC) milling or 3D printing techniques and are generally small.…”

“…With this structure, it is difficult to achieve large input couplings and, therefore, it is impossible to obtain a wide bandwidth (FBW > 10%). The slow wave solution presented in [45] allows the design of GGW bandpass filters with different bandwidths, using the cut-off frequency of the GGW and band-stop effect of the quasi-periodic transverse corrugations inside the GGW. However, this method requires a large number of corrugations to achieve a high level of rejection in the out-of-band region, which makes it difficult to determine the upper edge of the bandwidth and increases the size of the filter.…”